All ventilation systems must be designed in accordance with the National Construction Code (NCC), which in turn requires compliance with Australian Standards 1668.1 and 1668.2 for mechanical ventilation systems.

BASIX calculations are based on AS1668.2 minimum airflow requirements and generally assume fan efficiency higher than the NCC minimum.

Internal ventilation options?

The most efficient option is natural ventilation, typically via windows that can be opened.

In general, individual fans without ducting are likely to be the most efficient of the mechanical ventilation options. However, moist air vented to the roof space by individual fans without ducting can increase the risks of building condensation, especially if the roof material is continuous (such as metal roofing).

Ducted individual fans are not much worse than those without ducting in terms of energy efficiency, as long as the intake, ducting and discharge are reasonably sized. Ideally, from a heating and cooling perspective, fans should have automatic dampers or shutters so that air does not leak through them when they are not operating.

A fan with some form of operation control such as manual on/off or interlocking to the light switch, will be considerably more efficient than a continuously operating fan.